An electrical transformer is a device for taking electrical power from a source of alternating voltage (with a zero average value) and delivering it to one or more (primarily resistive) loads as efficiently as possible. It may also alter the root-mean-square (rms) voltage from the source value to potentially different values for each load, and it may provide galvanic isolation of each load from one another and from the source. Power efficiency and regulation are relevant to the performance of electrical transformers in numerous applications.